This is almost 100% source compatible with Qt 5. Exceptions are
* Stability of references for large or non movable types
* taking a PMF for types that are now overloaded with r-value references
in QVector
* The missing prepend optimization in QVector (that is still planned
to come for Qt 6)
Change-Id: I96d44553304dd623def9c70d6fea8fa2fb0373b0
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>